Method and device for displaying a velocity vector of an aircraft

ABSTRACT

The device ( 1 ) comprises a first means ( 3 ) for measuring the effective value of the velocity vector of the aircraft, a computing unit ( 4 ) which determines a display value automatically and repetitively and which comprises a filtering means ( 6 ) which filters the value measured by the first means ( 3 ) so as to form a first term, a display unit ( 7 ) for presenting on a screen ( 2 ) a characteristic sign illustrating the velocity vector whose position on the screen ( 2 ) is representative of the display value, and a second means ( 9 ) for determining the derivative of a velocity vector controlled by an aircraft pilot. The computing unit ( 4 ) further comprises a computing means ( 10 ) which determines a second term from the derivative of the controlled velocity vector and a summator ( 12 ) which sums the first and second terms so as to form the display value.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method and to a device fordisplaying a velocity vector of an aircraft.

DESCRIPTION OF THE PRIOR ART

[0002] It is known that the display of a velocity vector which isintended to indicate the point in space toward which the aircraft isoriented (without however being representative of the amplitude of thevelocity) may, in particular, be produced on a display screen of theaircraft's instrument panel or of a head-up display visor.

[0003] When an aircraft which is fit with such a device passes through aregion of turbulence, the position of said velocity vector on thedisplay screen is affected by the turbulence. Similarly, when theaircraft jettisons load, its flight path is temporarily disturbed, whichleads to a variation in the position of the velocity vector displayed.However, in this case, at the end of a relatively short time, theaircraft returns to its initial flight path.

[0004] When the pilot notices a variation in the position of thevelocity vector on the screen, he is tempted to act on a control column,in order to return the aircraft to its initial flight path. Since thedisturbances in question (turbulence, jettisoning, etc.) have a limitedeffect over time on the flight path of the aircraft, the consequence ofsuch a pilot action is a lasting modification of the flight path, thatis to say an effect opposite to the desired effect. The pilot must, inthis case, carry out a second action on the column, in a directionopposite to the direction of his first action, in order to return theaircraft to its initial flight path. In some situations, especially whenpassing through a region of turbulence, this second action may lead totoo great a correction of the flight path. Other actions on the columnare then necessary to succeed in stabilizing the aircraft on the desiredflight path.

[0005] Of course, such a phenomenon, which can be likened to “pilotinduced oscillations” must be prevented, since it may especially lead toaccelerated fatigue of the aircraft structure and it monopolizes theattention of the pilot in phases of flight where he may have toundertake other actions.

[0006] A known solution making it possible to overcome this problemconsists in filtering the display of the velocity vector by means of alow-pass filter having a time constant of between a few tenths of asecond and a few seconds. This makes it possible to prevent theaforementioned phenomenon, but the result of this is a new problem: whenthe pilot desires to modify the flight path by acting on the controlcolumn, this low-pass filter introduces a delay between the modificationof the flight path resulting from the action on the control column andthe variation in the display of the velocity vector on the screen. Thislack of ability to react hampers the judgement by the pilot of theeffect of his action on the control column, which makes mastering suchan action very difficult. This is because, if the pilot acts, forexample, for too long on the control column, there is a risk ofovershooting the desired flight path, which may lead to “pilot inducedoscillations”, as described above.

[0007] Moreover, document EP-0 366 164 proposes another solutionconsisting in displaying either a velocity vector corresponding to theactions of the pilot (controlled velocity vector), or the measuredvelocity vector. A switching device makes it possible to display one orother of these velocity vectors. Under “normal” flight conditions,corresponding to predefined velocity ranges, angle of incidence, loadfactor, etc., the controlled velocity vector is displayed. On the otherhand, when the aircraft operates outside these “normal” flightconditions, the measured velocity vector is displayed. During theswitching between these two velocity vectors, filtering is applied toavoid discontinuity of the display.

[0008] However, this known solution has drawbacks. In particular, twodifferent information items are displayed with a single symbol, whichrequires logic for changing over between these two information items,which may lead to possible problems of transition, of choice which isnot always optimum between one or other information item, etc.

SUMMARY OF THE INVENTION

[0009] The object of the present invention is to overcome thesedrawbacks. It relates to a method for displaying a velocity vector of anaircraft, which makes it possible to generate a display:

[0010] which remains stable, even in the case of temporary disturbancesin the flight path of said aircraft, due for example to turbulence or tojettisoning of load; and

[0011] which is highly reactive, during consecutive variations of flightpath, to at least one action of a pilot on a control member or column ofthe aircraft.

[0012] To this end, according to the invention, said method according towhich:

[0013] a display value representing the value of said velocity vector tobe displayed and dependent on a first term which comprises a measuredand filtered value of the velocity vector is determined automaticallyand repetitively; and

[0014] a characteristic sign illustrating said velocity vector, theposition of which on said display screen is representative of saiddisplay value, is presented on a display screen,

[0015] is noteworthy in that, in order to determine said display value:

[0016] the value of the time derivative of a velocity vector which iscontrolled by the pilot of said aircraft is determined;

[0017] a second term is calculated from said value of the derivative ofthe controlled velocity vector; and

[0018] the sum of said first and second terms is calculated so as toform said display value.

[0019] Thus, by virtue of the invention, the aforementioned drawbackscan be overcome. This is because:

[0020] said first term which takes into account a filtered value of the(effective) measured velocity vector makes it possible to obtain astable display of the velocity vector, even in the case of temporarydisturbances of the flight path; and

[0021] said second term which takes into account the derivative of thecontrolled velocity vector guarantees a suitable and high reactivity ofthe velocity vector display during variations in the flight path due topilot actions, especially on a control column.

[0022] Furthermore, by virtue of continuously taking account (via asummator) of these two terms, and therefore of the measured velocityvector and of the controlled velocity vector, no transition logic isneeded, unlike the solution proposed by the aforementioned document EP-0366 164.

[0023] Advantageously:

[0024] said first term γ₁ is calculated from the following expression:

γ₁=[1/(1τ₁ +xs)]×γ_(mes)

[0025] in which:

[0026] s is the Laplace transform;

[0027] τ₁ is a predetermined time constant; and

[0028] γ_(mes) represents the measured velocity factor; and

[0029] said second term γ₂ is calculated from the following expression:

γ₂=[τ₂/(1+τ₃ xs)]×γ_(der)

[0030] in which:

[0031] s is the Laplace transform;

[0032] τ₂ and τ₃ are predetermined time constants; and

[0033] γ_(der) represents the derivative of the velocity vectorcontrolled by the pilot.

[0034] According to the invention, the time constants τ₁, τ₂ and τ₃ maybe determined as a function of various parameters, in particular as afunction of the aircraft mass. These time constants may of course bedifferent from each other. However, in a simplified embodiment, saidtime constants τ₁, τ₂ and τ₃ are equal.

[0035] Moreover, advantageously, in order to determine the component ofthe display value in a (first) vertical direction, the derivative of thecontrolled velocity vector is determined by taking account of one of thefollowing controls:

[0036] control of the load factor of the aircraft;

[0037] control of the inclination of the aircraft; and

[0038] control of the derivative of the inclination of the aircraft.

[0039] By taking account of the control of the aircraft load factor,preferably, the derivative γ_(der) of the controlled velocity vectorγ_(com) is calculated from the controlled variation of the load factorΔN_(zpil), by using the following expression:

γ_(der)=(g/V)×ΔN _(zpil)

[0040] in which:

[0041] g is the acceleration due to gravity; and

[0042] V is the velocity of the aircraft.

[0043] Moreover, advantageously, in order to determine the component ofthe display value in a second direction which is lateral to the aircraftand orthogonal to said vertical direction, the derivative of thecontrolled velocity vector is determined from the control of the rollrate (angular velocity over the roll axis) of the aircraft.

[0044] The present invention also relates to a device for displaying avelocity vector of an aircraft and implementing the aforementionedmethod.

[0045] According to the invention, said device of the type comprising:

[0046] a first means for measuring the effective value of the velocityvector of the aircraft;

[0047] a computing unit for determining, automatically and repetitively,a display value representing the value of the velocity vector to bedisplayed, said computing unit comprising a filtering means whichfilters the value measured by said first means so as to form a firstterm; and

[0048] a display unit for presenting on a display screen acharacteristic sign illustrating said velocity vector whose position onsaid display screen is representative of said display value,

[0049] is remarkable in that it comprises, in addition, a second meansfor determining the time derivative of a velocity vector controlled byan aircraft pilot, and in that said computing unit further comprises:

[0050] a computing means which determines a second term from saidderivative of the controlled velocity vector; and

[0051] a summator which sums said first and second terms so as to formsaid display value.

[0052] Moreover, the present invention relates to an aircraft, inparticular a civil transport aircraft, which is fit with theaforementioned device.

BRIEF DESCRIPTION OF THE DRAWING

[0053] The single FIGURE of the appended drawing will make it clear tounderstand how the invention can be embodied. This FIGURE represents theblock diagram of a device according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

[0054] The device 1 according to the invention and shown schematicallyin the FIGURE is on board an aircraft, for example a transport aircraft(not shown) and is intended to display a velocity vector of the aircrafton a display screen 2 of the latter, for example a screen of theinstrument panel or a head-up display (HUD) visor.

[0055] Said device 1 comprises, in a known manner:

[0056] a means 3, of the usual type, for measuring the effective valueof the velocity vector of the aircraft;

[0057] a computing unit 4 for determining, automatically andrepetitively, a display value γ_(dis) representing the value of thevelocity vector to be displayed. Said computing unit 4 is connected tothe means 3 by a connection 5 and comprises a filtering means 6,specified below, which filters the value measured by said means 3 so asto form a first term γ₁; and

[0058] a display unit 7 which is connected by a connection 8 to thecomputing unit 4, which comprises the display screen 2 and which isintended to present on this display screen 2 a characteristic signillustrating said velocity vector, the position of which on said displayscreen 2 is representative of said display value γ_(dis).

[0059] Within the context of the present invention, the filtering(indicated above) of the measured velocity vector concerns an actionwhich consists in filtering the value of the measured velocity vector bymeans of a low-pass filter (having a time constant of, for example,between a few tenths of a second and a few seconds), in order to makethis value insensitive to temporary disturbances (for example less thana few [3, 4, etc.] seconds) of the flight path of the aircraft.

[0060] According to the invention, said device 1 comprises in addition,a means 9, of the usual type, for determining the (time) derivative of a(controlled) velocity vector controlled by an aircraft pilot, and saidcomputing unit 4 further comprises:

[0061] a computing means 10 which is connected by a connection 11 to themeans 9 and which determines a second term γ₂ from said derivative ofthe controlled velocity vector; and

[0062] a summator 12 which is connected by connections 13 and 14respectively to the filtering means 6 and to the computing means 10 andwhich sums said first and second terms so as to form said display valueγ_(dis).

[0063] Thus, by virtue of the invention, the display value γ_(dis) whichis used to produce the display comprises said first and second terms γ₁and γ₂ which are such that:

[0064] said first term γ₁ which takes into account a filtered value ofthe (effective) measured velocity vector makes it possible to obtain astable display of the velocity vector even in the case of temporarydisturbances of the flight path, as indicated above; and simultaneously

[0065] said second term γ₂ which takes into account the derivative ofthe controlled velocity vector guarantees a suitable and high reactivityof the velocity vector display, during variations in the flight path dueto pilot actions, especially on a control column, and this in spite ofthe aforementioned filtering which is provided according to theinvention (but which is limited to said first term γ₁).

[0066] Furthermore, by virtue of continuously taking account (via thesummator 12) of these two terms γ₁ and γ₂, and therefore of the measuredvelocity vector and of the controlled velocity vector, no transitionlogic is needed, unlike, for example, the solution proposed by theaforementioned document EP-0 366 164.

[0067] In a preferred embodiment, the means 6 calculates said first termγ₁ from the following expression:

γ₁=[1/(1+τ_(xs))]×γ_(mes)

[0068] in which:

[0069] s is the Laplace transform;

[0070] τ₁ is a predetermined time constant; and

[0071] γ_(mes) represents the measured velocity factor.

[0072] Furthermore, preferably, said means 10 calculates said secondterm γ₂ from the following expression:

γ₂=[τ₂/(1+τ₃ xs)]×γ_(der)

[0073] in which:

[0074] s is the Laplace transform;

[0075] τ₂ and τ₃ are predetermined time constants; and

[0076] γ_(der) represents the derivative of the velocity vector γ_(com)controlled by the pilot.

[0077] In this case, the display value γ_(dis) which is transmitted bythe computing unit 4 to the display unit 7 and which is formed by thesum of said first and second terms γ₁ and γ₂ can be written:

γ_(dis)=[1/(1+τ₁ xs)]×γ_(mes)+[τ₂/(1+τ₃ xs)]×γ_(der).

[0078] According to the invention, the time constants τ₁, τ₂ and τ₃ maybe determined as a function of various parameters, in particular as afunction of the aircraft mass. These time constants may be differentfrom each other. However, in a simplified embodiment, said timeconstants τ₁, τ₂ and τ₃ are regarded as being equal.

[0079] It will be noted that satisfactory results are especiallyobtained with a filtering time constant τ₁ substantially equal to 0.6seconds and time constants τ₂ and τ₃ substantially equal to two seconds,in the case of a heavy or fairly heavy aircraft, for example a transportaircraft.

[0080] Moreover, the value γ_(der) is determined as a function of thereference values (or controls) entered by the pilot, especially by meansof the normal control column of the aircraft. Depending on the axis inquestion, these reference values may be expressed in different units.Thus, by way of nonlimiting example, along the vertical z-axis of acoordinate system linked to the aircraft (vertical slope of theaircraft), said reference values may be entered as a load factor N_(z),as a slope derivative, as a slope, etc. When the reference value alongthis z-axis is expressed as a slope derivative, the value of τ_(der) isequal to this reference value. When it is expressed as a slope, thevalue of γ_(der) is equal to the derivative of said reference value.

[0081] When it is expressed in another unit, it is worth converting it.For example, where it corresponds to a load factor N_(z), it can beconverted as indicated below.

[0082] It is known that the derivative γ′ of the velocity vector issubstantially equal to the following value:

γ′≈(g/V)×ΔN _(z)

[0083] where ΔN_(z) is the variation in the load factor N_(z), g is theacceleration due to gravity and V is the velocity of the aircraft.

[0084] From this, the following expression can be deduced:

γ_(der)≈(g/V)×ΔN _(zpil)

[0085] in which ΔN_(zpil) represents the variation in the load factorwhich is controlled by the pilot and which corresponds to the movementof the control column (or member).

[0086] In this preferred embodiment, we therefore have for the z-axis:

γ_(dis)=[1/(1+τ₁ xs)]γ_(mes)+[τ₂/(1+τ ₃ xs)]×(g/V)×ΔN_(zpil);

[0087] where

[0088] *if τ₁=τ₂=τ₃=τ:

τ_(dis)=[1/(1+τxs)]×γ_(mes)+[τ/(1+τxs)]×(g/v)×ΔN _(zpil).

[0089] Along the y-axis (which is lateral to the aircraft and orthogonalto the vertical axis z) of a coordinate system associated with theaircraft (corresponding to the lateral parameters of the aircraft,especially course, side slip, roll), the reference values input by thepilot are, preferably, expressed in terms of roll rate, without thatbeing limiting. This roll rate is an angular velocity over the rollaxis, which makes it possible to determine at any instant the roll angleof the aircraft. A non zero roll angle leads to turning of the aircraftand the mechanical laws of flight make it possible consequently tocalculate an acceleration Ay along said y-axis. In terms of units,acceleration is equivalent to a load factor. In a manner similar to theaforementioned example of transforming the load factor N_(z) into avalue γ_(der) along the z-axis, this acceleration Ay may be transformedinto a value γ_(der) along the y-axis.

[0090] Moreover, along the x-axis (which represents the longitudinalaxis of the aircraft and which is therefore orthogonal to the z- andy-axes) of a coordinate system associated with the aircraft, thereference values entered by the pilot mainly correspond to the thrust ofthe engines, controlled, for example, by means of the throttle. Thisthrust leads to an acceleration Ax along the longitudinal x-axis of theaircraft, which can be transformed into a value γ_(der) along thisx-axis, in a manner similar to the aforementioned transformationsrelating to the y- and z-axes.

[0091] Furthermore, it will be noted that, in the case of an HUD visor,the x-axis being perpendicular to the plane of said HUD visor, it ispossible, in order to guarantee the clarity and readability of thedisplay, to return the parameters associated with this x-axis to adisplay along the z-axis by a normal transformation called “totalslope”.

1. A method for displaying a velocity vector of an aircraft, a method inwhich: a display value representing the value of said velocity vector tobe displayed and dependent on a first term which comprises a measuredand filtered value of the velocity vector is determined automaticallyand repetitively; and a characteristic sign illustrating said velocityvector, the position of which on said display screen is representativeof said display value, is presented on a display screen, wherein, inorder to determine said display value: the value of the time derivativeof a velocity vector which is controlled by the pilot of said aircraftis determined; a second term is calculated from said value of thederivative of the controlled velocity vector; and the sum of said firstand second terms is calculated so as to form said display value.
 2. Themethod as claimed in claim 1, wherein said first term γ₁ is calculatedfrom the following expression: γ₁=[1/(1+τ ₁ xs)]×γ_(mes) in which: s isthe Laplace transform; τ₁ is a predetermined time constant; and γ_(mes)represents the measured velocity factor.
 3. The method as claimed inclaim 1, wherein said second term γ₂ is calculated from the followingexpression: γ₂=[τ₂(1+τ₃ xs)]×γ_(der) in which: s is the Laplacetransform; τ₂ and τ₃ are predetermined time constants; and γ_(der)represents the derivative of the velocity vector controlled by thepilot.
 4. The method as claimed in claim 2, wherein said time constantsτ₁, τ₂ and τ₃ are equal.
 5. The method as claimed in claim 1, wherein,in order to determine the component of the display value in a verticaldirection, the derivative of the controlled velocity vector isdetermined by taking account of one of the following controls: controlof the load factor of the aircraft; control of the inclination of theaircraft; and control of the derivative of the inclination of theaircraft.
 6. The method as claimed in claim 3, wherein the derivativeγ_(der) of the controlled velocity vector is calculated from thecontrolled variation of the load factor ΔN_(zpil) of the aircraft, byusing the following expression: γ_(der)=(g/V)×ΔN _(zpil) in which: g isthe acceleration due to gravity; and V is the velocity of the aircraft.7. The method as claimed in claim 1, wherein, in order to determine thecomponent of the display value in a direction which is lateral to theaircraft and orthogonal to the vertical direction, the derivative of thecontrolled velocity vector is determined from the control of the rollrate.
 8. A device for displaying a velocity vector of an aircraft, saiddevice comprising: a first means for measuring the effective value ofthe velocity vector of the aircraft; a computing unit for determining,automatically and repetitively, a display value representing the valueof the velocity vector to be displayed, said computing unit comprising afiltering means which filters the value measured by said first means soas to form a first term; and a display unit for presenting on a displayscreen a characteristic sign illustrating said velocity vector whoseposition on said display screen is representative of said display value,which device comprises, in addition, a second means for determining thetime derivative of a velocity vector controlled by an aircraft pilot,and in that said computing unit further comprises: a computing meanswhich determines a second term from said derivative of the controlledvelocity vector; and a summator which sums said first and second termsso as to form said display value.
 9. An aircraft, which comprises adisplay device such as the one specified in claim 8.